The long-term goals of the proposed program are to define mechanisms of host reaction against schistosomula and to elucidate the processes by which developing schistosomula become insusceptible to immune attack. These studies are to be carried out in laboratory mice infected with Schistosoma mansoni. The specific goals of the proposed work are as follows: a) to examine the immune inflammatory response to challenge schistosomula for evidence of an exudative component. b) to study mechanisms of granulocyte chemotoxis and adherence to schistosomula. c) to identify the subclasses and antigenic specificities of antibodies involved in schistosomulum rejection. d) to identify the effector cells involved in schistosomulum rejection. e) to study the developmental changes occurring in schistosomula which make them refractory to immune damage. It is hoped that the proposed studies will lead to a more detailed understanding of the effector mechanism of protective immunity against schistosomes in vivo as well as the means by which established parasites evade the immune response. This information is relevant to the formulation of strategies for vaccinating against schistosome infection.